Along with technical development and increased demands on mobile devices, secondary batteries have been consumed more and more as energy sources. In the past, nickel cadmium batteries or hydrogen ion batteries have been used as secondary batteries, but recently, lithium ion batteries and lithium polymer batteries with a high energy density are widely used.
Among these secondary batteries, a lithium secondary battery using lithium transition metal oxide, lithium complex oxide or the like as a positive electrode active material and ensuring high output and capacity receives a great interest. Generally, a lithium secondary battery has a structure in which an electrode assembly composed of a positive electrode, a separator and a negative electrode is embedded in a sealed container together with an electrolyte.
Meanwhile, the lithium secondary battery includes a positive electrode, a negative electrode, and a separator and an electrolyte interposed therebetween. Depending on which material is used as a positive electrode active material and a negative electrode active material, the lithium secondary battery is classified into a lithium ion battery (LIB), a polymer lithium ion battery (PLIB) and so on. Typically, electrodes of these lithium secondary batteries are formed by applying a positive electrode active material or a negative electrode active material to a current collector such as aluminum or copper sheet, mesh, film, or foil, and then drying the same.
In the secondary battery module, cells accommodated in each cartridge by performing welding, bolting, riveting or the like between cell leads. In addition, when cells are arranged in series or in parallel in the secondary battery module, three members, namely the positive electrode lead made of aluminum, the negative electrode lead made of copper and the bus bar made of copper and disposed for sensing should be electrically connected by using the above method.
According to the prior art, there are various secondary battery modules, and the cartridges of the modules and bus bars for sensing are structured and located in different ways. For this reason, it is difficult to efficiently perform the connection work and the welding quality of the sensing structure is deteriorated. In addition, an unnecessary space of the secondary battery module should be provided for welding or the like, and resultantly energy density of the secondary battery module is lowered.
In addition secondary battery modules used in energy storage devices or power storage devices have been developed for designing developing secondary battery modules as compact as possible in order to increase energy efficiency or density.
Meanwhile, in the configuration of a general secondary battery module, when welding (especially, laser welding) is performed to electrode leads (Al)(Cu) and bus bars (Cu) of cells, due to the different melting points of materials, generally, base materials are disposed in the order of an aluminum lead, a copper lead and bus bars, and then laser is irradiated from a cell lead for welding. However, if welding is performed in this order, the cell lead may be deformed first by the laser.